全文获取类型
收费全文 | 379篇 |
免费 | 3篇 |
国内免费 | 5篇 |
专业分类
化学 | 188篇 |
晶体学 | 2篇 |
力学 | 2篇 |
数学 | 42篇 |
物理学 | 153篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2016年 | 4篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1987年 | 7篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 8篇 |
1973年 | 4篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1967年 | 4篇 |
1966年 | 3篇 |
1964年 | 2篇 |
1939年 | 2篇 |
1929年 | 4篇 |
1927年 | 2篇 |
排序方式: 共有387条查询结果,搜索用时 93 毫秒
1.
Several models have been developed in order to categorize the numerous expressions that people use in order to describe their emotional experiences. The focus of the present study is on one of these theoretical classifications proposed by Pekrun (1992) specifically concerning emotions which are directly related to learning and achievement in mathematics. In his model, emotions are classified according to their valence (positive vs. negative) and their level of activation. In testing the assumptions of this model, we investigated students' enjoyment, anxiety, anger and boredom experienced before, during, and after the completion of a math test. Correspondence analyses which were used to generate a graphical illustration of structural interrelationships between these emotions provide empirical support for the theoretical classification. 相似文献
2.
P. Kratzer E. Penev M. Scheffler 《Applied Physics A: Materials Science & Processing》2002,75(1):79-88
We demonstrate how first-principles calculations using density-functional theory (DFT) can be applied to gain insight into
the molecular processes that rule the physics of materials processing. Specifically, we study the molecular beam epitaxy (MBE)
of arsenic compound semiconductors. For homoepitaxy of GaAs on GaAs (001), a growth model is presented that builds on results
of DFT calculations for molecular processes on the β2-reconstructed GaAs (001) surface, including adsorption, desorption,
surface diffusion, and nucleation. Kinetic Monte Carlo simulations on the basis of the calculated energetics enable us to
model MBE growth of GaAs from beams of Ga and As2 in atomistic detail. The simulations show that island nucleation is controlled by the reaction of As2 molecules with Ga adatoms on the surface. The analysis reveals that the scaling laws of standard nucleation theory for the
island density as a function of growth temperature are not applicable to GaAs epitaxy. We also discuss heteroepitaxy of InAs
on GaAs (001), and report first-principles DFT calculations for In diffusion on the strained GaAs substrate. In particular,
we address the effect of heteroepitaxial strain on the growth kinetics of coherently strained InAs islands. The strain field
around an island is found to cause a slowing down of material transport from the substrate towards the island, and thus helps
to achieve more homogeneous island sizes.
Received: 2 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
3.
All-electron full-potential linearized augmented plane-wave calculations of the surface energy, work function, and interlayer spacings of close-packed metal surfaces are presented, in particular, for the free-electron-like metal surfaces, Mg(0 0 0 1) and Al(1 1 1), and for the transition metal surfaces, Ti(0 0 0 1), Cu(1 1 1), Pd(1 1 1), and Pt(1 1 1). We investigate the convergence of the surface energy as a function of the number of layers in the slab, using the Cu(1 1 1) surface as an example. The results show that the surface energy, as obtained using total energies of the slab and bulk from separate calculations, converges well with respect to the number of layers in the slab. Obviously, it is necessary that bulk and surface calculations are performed with the same high accuracy. Furthermore, we discuss the performance of the local-density and generalized gradient approximations for the exchange-correlation functional in describing the various surface properties. 相似文献
4.
Werner Schulze und Manfred Scheffler 《Fresenius' Journal of Analytical Chemistry》1967,226(5):395-401
Zusammenfassung Um Material zur Deutung des Mechanismus der Sorption von Sr2+-Ionen an Eisen(III)-hydroxid zu gewinnen, werden Meßreihen mitgeteilt, in denen die pH-Abhängigkeit der Sorption sowie deren Beeinflussung bei Fällung mit verschiedenen Basen (NaOH, Ammoniak, Trimethylamin, Benzylamin) untersucht wird. Aus den charakteristischen Unterschieden der Sorptionskurven muß gefolgert werden, daß die Art der Base für die Sorption eine wichtige Rolle spielt.
Summary The sorption of Sr2+ ions on iron(III) hydroxide was studied as a function of the pH, of the precipitating reagent (NaOH, ammonium hydroxide, benzylamine, trimethylamine), of the temperature and of the total concentration.The curves of the relative sorption vs. pH are found to show characteristic differences which have to be explained in a detailed theory of the mechanism.相似文献
5.
L. Goetz E. Sabbioni E. Marafante J. Edel-Rade C. Birattari M. Bonardi 《Journal of Radioanalytical and Nuclear Chemistry》1981,67(1):183-192
Carrier-free201+202Tl have been produced in the cyclotron by (p, xn) reactions on mercury targets and used as a trcer for thallium in metallobiochemistry
of heavy metal pollution. The separation of201+202Tl radioisotopes from Hg involved a solvent extraction method leading to labelled univalent Tl(I) ions. This radioactive solution
was used to prepare different201+202Tl labelled compounds such as inorganic Tl(III) ions and organic dimethylthallium. Quality controls have been applied directly
on the different radioactive solutions immediately before their administrations to rats in order to ensure that thallium had
the chemical form expected. A summary of the main results concerning different aspects of the metabolic investigations on
rats such as absorption, retention, excretion, transplacental transport and influence of the different chemical forms of thallium
on its metabolism is also reported. 相似文献
6.
Frederick J. Goetz 《Journal of heterocyclic chemistry》1967,4(1):80-84
A definite tautomeric relationship has been found between 2-arylbenzothiazolines (I) and 2-(benzylideneamino)thiophenols (II). In a reaction characteristic of the closed ring structure (I), 2-arylbenzothiazolines were oxidized in high yield with benzoyl peroxide to the corresponding 2-arylbenzothiazoles (III). Reactions characteristic of the open ring structure (II) include the formation of the potassium salt of the open ring structure (IV) by reaction of 2-arylbenzothiazolines with potassium t-butoxide in toluene and oxidation of 2-arylbenzothiazolines to bis-[2-(benzylideneamino)phenyl] disulfides (V) by hydrogen peroxide in methanol. 相似文献
7.
8.
9.
10.